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          <h1>Using Shared Data with Vert.x</h1>
          
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          <ul class="sectlevel1">
<li><a href="#_using_shared_data_with_vert_x">Using Shared Data with Vert.x</a>
<ul class="sectlevel2">
<li><a href="#_local_shared_maps">Local shared maps</a></li>
<li><a href="#_cluster_wide_asynchronous_maps">Cluster-wide asynchronous maps</a></li>
<li><a href="#_cluster_wide_locks">Cluster-wide locks</a></li>
<li><a href="#_cluster_wide_counters">Cluster-wide counters</a></li>
</ul>
</li>
</ul>
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      <div class="col-sm-12 col-md-pull-3 col-md-9">
        <div class="toc hidden-md hidden-lg">
          <h2>Table of Contents</h2>
          <ul class="sectlevel1">
<li><a href="#_using_shared_data_with_vert_x">Using Shared Data with Vert.x</a>
<ul class="sectlevel2">
<li><a href="#_local_shared_maps">Local shared maps</a></li>
<li><a href="#_cluster_wide_asynchronous_maps">Cluster-wide asynchronous maps</a></li>
<li><a href="#_cluster_wide_locks">Cluster-wide locks</a></li>
<li><a href="#_cluster_wide_counters">Cluster-wide counters</a></li>
</ul>
</li>
</ul>
        </div>
        <div class="sect1">
<h2 id="_using_shared_data_with_vert_x">Using Shared Data with Vert.x</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Shared data contains functionality that allows you to safely share data between different parts of your application,
or different applications in the same Vert.x instance or across a cluster of Vert.x instances.</p>
</div>
<div class="paragraph">
<p>Shared data includes local shared maps, distributed, cluster-wide maps, asynchronous cluster-wide locks and
asynchronous cluster-wide counters.</p>
</div>
<div class="admonitionblock important">
<table>
<tr>
<td class="icon">
<div class="title">Important</div>
</td>
<td class="content">
The behavior of the distributed data structure depends on the cluster manager you use. Backup
(replication) and behavior when a network partition is faced are defined by the cluster manager and its
configuration. Refer to the cluster manager documentation as well as to the underlying framework manual.
</td>
</tr>
</table>
</div>
<div class="sect2">
<h3 id="_local_shared_maps">Local shared maps</h3>
<div class="paragraph">
<p><code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/LocalMap.html">Local shared maps</a></code> allow you to share data safely between different event
loops (e.g. different verticles) in the same Vert.x instance.</p>
</div>
<div class="paragraph">
<p>Local shared maps only allow certain data types to be used as keys and values. Those types must either be immutable,
or certain other types that can be copied like <code><a href="../../groovydoc/io/vertx/groovy/core/buffer/Buffer.html">Buffer</a></code>. In the latter case the key/value
will be copied before putting it in the map.</p>
</div>
<div class="paragraph">
<p>This way we can ensure there is no <em>shared access to mutable state</em> between different threads in your Vert.x application
so you don&#8217;t have to worry about protecting that state by synchronising access to it.</p>
</div>
<div class="paragraph">
<p>Here&#8217;s an example of using a shared local map:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">import io.vertx.groovy.core.buffer.Buffer

def sd = vertx.sharedData()

def map1 = sd.getLocalMap("mymap1")

map1.put("foo", "bar")

def map2 = sd.getLocalMap("mymap2")

map2.put("eek", Buffer.buffer().appendInt(123))

// Then... in another part of your application:

map1 = sd.getLocalMap("mymap1")

def val = map1.get("foo")

map2 = sd.getLocalMap("mymap2")

def buff = map2.get("eek")</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_cluster_wide_asynchronous_maps">Cluster-wide asynchronous maps</h3>
<div class="paragraph">
<p>Cluster-wide asynchronous maps allow data to be put in the map from any node of the cluster and retrieved from any
other node.</p>
</div>
<div class="paragraph">
<p>This makes them really useful for things like storing session state in a farm of servers hosting a Vert.x web
application.</p>
</div>
<div class="paragraph">
<p>You get an instance of <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/AsyncMap.html">AsyncMap</a></code> with
<code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/SharedData.html#getClusterWideMap(java.lang.String,%20io.vertx.core.Handler)">getClusterWideMap</a></code>.</p>
</div>
<div class="paragraph">
<p>Getting the map is asynchronous and the result is returned to you in the handler that you specify. Here&#8217;s an example:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">def sd = vertx.sharedData()

sd.getClusterWideMap("mymap", { res -&gt;
  if (res.succeeded()) {
    def map = res.result()
  } else {
    // Something went wrong!
  }
})</code></pre>
</div>
</div>
<div class="sect3">
<h4 id="_putting_data_in_a_map">Putting data in a map</h4>
<div class="paragraph">
<p>You put data in a map with <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/AsyncMap.html#put(java.lang.Object,%20java.lang.Object,%20io.vertx.core.Handler)">put</a></code>.</p>
</div>
<div class="paragraph">
<p>The actual put is asynchronous and the handler is notified once it is complete:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">map.put("foo", "bar", { resPut -&gt;
  if (resPut.succeeded()) {
    // Successfully put the value
  } else {
    // Something went wrong!
  }
})</code></pre>
</div>
</div>
</div>
<div class="sect3">
<h4 id="_getting_data_from_a_map">Getting data from a map</h4>
<div class="paragraph">
<p>You get data from a map with <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/AsyncMap.html#get(java.lang.Object,%20io.vertx.core.Handler)">get</a></code>.</p>
</div>
<div class="paragraph">
<p>The actual get is asynchronous and the handler is notified with the result some time later</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">map.get("foo", { resGet -&gt;
  if (resGet.succeeded()) {
    // Successfully got the value
    def val = resGet.result()
  } else {
    // Something went wrong!
  }
})</code></pre>
</div>
</div>
<div class="sect4">
<h5 id="_other_map_operations">Other map operations</h5>
<div class="paragraph">
<p>You can also remove entries from an asynchronous map, clear them and get the size.</p>
</div>
<div class="paragraph">
<p>See the <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/AsyncMap.html">API docs</a></code> for more information.</p>
</div>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_cluster_wide_locks">Cluster-wide locks</h3>
<div class="paragraph">
<p><code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/Lock.html">Cluster wide locks</a></code> allow you to obtain exclusive locks across the cluster -
this is useful when you want to do something or access a resource on only one node of a cluster at any one time.</p>
</div>
<div class="paragraph">
<p>Cluster wide locks have an asynchronous API unlike most lock APIs which block the calling thread until the lock
is obtained.</p>
</div>
<div class="paragraph">
<p>To obtain a lock use <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/SharedData.html#getLock(java.lang.String,%20io.vertx.core.Handler)">getLock</a></code>.</p>
</div>
<div class="paragraph">
<p>This won&#8217;t block, but when the lock is available, the handler will be called with an instance of <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/Lock.html">Lock</a></code>,
signifying that you now own the lock.</p>
</div>
<div class="paragraph">
<p>While you own the lock no other caller, anywhere on the cluster will be able to obtain the lock.</p>
</div>
<div class="paragraph">
<p>When you&#8217;ve finished with the lock, you call <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/Lock.html#release()">release</a></code> to release it, so
another caller can obtain it.</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">sd.getLock("mylock", { res -&gt;
  if (res.succeeded()) {
    // Got the lock!
    def lock = res.result()

    // 5 seconds later we release the lock so someone else can get it

    vertx.setTimer(5000, { tid -&gt;
      lock.release()
    })

  } else {
    // Something went wrong
  }
})</code></pre>
</div>
</div>
<div class="paragraph">
<p>You can also get a lock with a timeout. If it fails to obtain the lock within the timeout the handler will be called
with a failure:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">sd.getLockWithTimeout("mylock", 10000, { res -&gt;
  if (res.succeeded()) {
    // Got the lock!
    def lock = res.result()

  } else {
    // Failed to get lock
  }
})</code></pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_cluster_wide_counters">Cluster-wide counters</h3>
<div class="paragraph">
<p>It&#8217;s often useful to maintain an atomic counter across the different nodes of your application.</p>
</div>
<div class="paragraph">
<p>You can do this with <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/Counter.html">Counter</a></code>.</p>
</div>
<div class="paragraph">
<p>You obtain an instance with <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/SharedData.html#getCounter(java.lang.String,%20io.vertx.core.Handler)">getCounter</a></code>:</p>
</div>
<div class="listingblock">
<div class="content">
<pre class="prettyprint highlight"><code class="language-groovy" data-lang="groovy">sd.getCounter("mycounter", { res -&gt;
  if (res.succeeded()) {
    def counter = res.result()
  } else {
    // Something went wrong!
  }
})</code></pre>
</div>
</div>
<div class="paragraph">
<p>Once you have an instance you can retrieve the current count, atomically increment it, decrement and add a value to
it using the various methods.</p>
</div>
<div class="paragraph">
<p>See the <code><a href="../../groovydoc/io/vertx/groovy/core/shareddata/Counter.html">API docs</a></code> for more information.</p>
</div>
</div>
</div>
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